I. Field of the Invention
The present invention relates generally to patient monitoring equipment in the form of a probe attached to the patient for measuring anaesthesia based on esophageal contractions and, specifically, to a quick disconnect connector which joins the probe with the remainder of the system located distant from the patient.
II. Description of the Prior Art
The present invention has application in monitoring the depth of anaesthesia of patients to whom anaesthetic or sedative drugs are administered. The term anaesthesia is used herein in its broadest sense and is intended to include not only anaesthesia for surgery, but also the lighter levels of anaesthesia or sedation used in critically ill patients receiving intensive care. The term anaesthetic is to be understood accordingly.
The response of individual patients to drugs is highly variable. Especially in the case of anaesthetic drugs, an anaesthetist is required to employ a considerable degree of clinical judgment in order to obtain an optimum effect. Clinical anaesthesia is not an "on-off" state but a state of unconsciousness and variable reflex suppression produced by one or more drugs. It is traditional to describe the degree of reflex suppression as the depth of anaesthesia. At present, the depth of anaesthesia is judged by the change in various clinical signs produced in response to surgical stimulus. It has been recognized to be of great assistance if some objective information were available indicating the depth of anaesthesia. Attempts have been made to use indirect measurements of a patient's vital physiological functions such as heart rate, blood pressure and electroencephalogram (EEG) waveforms to indicate depth of anaesthesia. However, none of these measurements alone has proved to be a sufficiently reliable index of depth of anaesthesia.
An article by P. Suppan in the British Journal of Anaesthesia, (1972) 44, p. 1263 describes the use of pulse rate as an indicator of depth of anaesthesia, and describes furthermore the use of a feed-back system to automatically control anaesthetic administration. The article also describes the possibility of using blood pressure as an indicator of the depth of anaesthesia, but there is no suggestion of the combined use of the parameters, or any suggestion that combining two or more measurements to produce a "score" can provide a more reliable indication of depth of anaesthesia.
M. Dubuis, D. E. Scott, and T. M. Savege, in an article in Annals Anaesthesia, France (1979) 3, p. 215, describe the use of EEG as an indicator of the after effects of anaesthesia.
Electronically processed EEG signals have been employed to monitor the level of electrical activity in the brain during anaesthesia. A review of this and other applications of EEG monitoring is given in Monitoring Cerebral Function (author P. F. Prior, published by Elsevoir (North-Holland Biomedical Press, 1979, Amsterdam).
Finally, J. S. Stewart in The Lancet (1969) 1, p. 1305 describes a monitoring system for drawing the attention of a clinician to a deteriorating condition of a patient, using a combination of various parameters, such as heart rate, blood pressure, and oxygen tension. There is, however, no suggestion in the Stewart article of the use of a similar system to measure depth of anaesthesia.
The patentees, John M. Evans and Colin C. Wise, of U.S. Pat. No. 4,502,490 issued Mar. 5, 1985 entitled "Patient Monitoring Equipment, Probe for Use Therewith, and Method of Measuring Anaesthesia Based on Oesophagal Contractions" have discovered that the muscular activity in the esophagus is related to the depth of anaesthesia. The disclosure of the aforesaid U.S. Pat. No. 4,502,490 is incorporated herein in its entirety and made a part hereof.
During light anaesthesia there is a great deal of smooth muscle activity in the form of periodic contractions. During deep anaesthesia there is little esophageal smooth muscle activity. Evans and Wise consistently observed this relationship between esophageal activity and depth of anaesthesia with most common anaesthetic agents. Changes in esophageal muscle activity cause corresponding changes in intralumenal esophageal pressure. Thus, by insertion of a balloon-type catheter, or some other suitable pressure probe, into the esophagus, and measuring the internal pressure in the esophagus, they found it is possible to obtain an indication of the depth of anaesthesia.
The pressure changes produced by esophageal contraction generally last 2-4 seconds and occur at frequencies of up to 4 or 5 per minute during light anaesthesia. Occasionally there are short periods of rapid contractions at rates of up to 15 per minute accompanied by high resting pressures between contractions.
Evans and Wise also discovered that, whether or not esophageal contractions are used as a measure of the degree of anaesthesia, increased reliability in the quantification by the anaesthetist of depth of anaesthesia can be obtained if a plurality of different bodily functions are observed, and a score value assigned to each in accordance with certain parameters.
The score values may then be summed to produce a total score indicative of the degree of anaesthesia of the patient.
As disclosed in the aforementioned U.S. Pat. No. 4,502,490, a convenient means of provoking the esophageal contractions is an air or liquid filled inflatable balloon inserted into the trachea or, more preferably, the esophagus. As explained in the patent, such a probe inserted into the esophagus can include a liquid filled monitor balloon and an air filled provoking balloon which is caused to expand and contract on a periodic basis. There are times which occur in the course of surgery when it is desired to rapidly either connect the air or gas filled balloon to the pressurized source or to disconnect it therefrom. It is desired that such a connection and disconnection be achieved in an easy and rapid action requiring only one hand for the procedure. In the past, connectors have been utilized which attached at one end to flexible plastic tubing which extended from the probe, the other end being tapered and intended for a press fit engagement with a metallic fitting adjacent the source of pressurized air or gas.
This arrangement often times required two hands to achieve, did not assure a uniformly tight connection each time, and was not of a positive nature such that it could become loosened with vibration and work itself free if left unattended.